Plug-type valves are well known in the prior art, particularly in the oil and gas industries where their positive sealing and superior flow characteristics are highly advantageous for controlling the flow of such fluids. As a result of the performance advantages of such valves, their design permits substantial reduction in plug mechanism size, and thus provides considerable cost savings, while still satisfying field operating requirements set by the user industries. Reduction in plug mechanism dimensions is normally achieved by utilizing inlet and outlet flow passages that are generally divergent in cross-section between the plug port and the pipe-connecting flange on the respective ends of the valve. Plug-type valves of this general configuration are disclosed in U.S. Pat. Nos. 2,609,174 and 2,708,094 to Heinen, now expired.
Providing the manifest advantages of reducing plug port size while still satisfying the flow rate requirements established for the valve, is a continuous objective of valve manufacturers and was a primary motivating factor for the present invention. More particularly, the present invention provides a surprisingly high flow rate capability, or from an alternative point of view, a surprisingly low pressure drop for a given flow rate. A common term used in the valve industry for specifying this important performance characteristic, is "C.sub.v " which is expressed in gallons per minute (GPM) and is defined as the rate of flow of water at 60.degree. F. with an insertion loss, or pressure drop of 1 psi.